This invention relates generally to a tracking lens for an optical sensor carried on an integrated chip (IC). More particularly, the invention provides a tracking lens integrated to the aperture plate of the IC so that the lens registers and aligns with the optical sensor.
Integrated chips with optical sensors are typically used for solid state computer input devices which rely on optical tracking to calculate relative displacement values to be communicated to an output converter. These input devices include optical pointing devices such as computer mice and trackballs. An IC with a reflective optical sensor is commercially available from Hewlett-Packard under the designation HDNS-2000, and is typically mounted on a printed circuit board (PCB) which is assembled with a lens plate. The assembly is mounted on a base plate of a housing for the computer input device. The base plate has an aperture operatively registered with and aligned with the magnified light from an LED for the optical sensor. Conventional assemblies of these components have relied on simple registration tabs and mating in the base plate, lens plate and IC mounted PCB to ensure that the aperture plate of the optical sensor, lens and aperture are operatively aligned.
With multiple components which must be assembled and registered together, any misalignment or registration error in such a conventional assembly is compounded and results in an unreliable or even inoperable pointing device. This can be a particular problem during manufacture since these components of pointing devices are most often assembled by hand.
Due to the multiplicity of parts which must be registered and assembled together these conventional assemblies are inefficient to manufacture and suffer from reliability flaws. With currently employed parts and techniques, there is no reliable way of ensuring repeatable and precise registration of the lens and base plate tracking aperture with the aperture plate of the IC optical sensor.
The present invention overcomes the problems of the prior art by providing a lens integrated into the aperture plate of an optical sensor equipped IC thus structurally integrating the lens to the IC in such a manner as to automatically align and register the lens with the optical sensor. The aperture plate is molded in one-piece with the lens at the appropriate location so that the lens aligns with the location of the optical sensor when the aperture plate is assembled to the IC. The lens and sensor are in fixed relation to one another since they are parts of the identical component, the IC, and any registration problems between the lens and sensor are eliminated.
The integrated lens is molded into the aperture plate. In order to ensure proper focus, the lens is spaced away from the optical sensor a predetermined distance. To accommodate the proper distance, the lens is molded at the end of an integrally molded column. The column includes structural features for enhanced strength and for proper positioning of the lens relative to the base plate of the housing. The column has two horizontal portions, a frusto-conical portion adjacent to the aperture plate and a cylindrical portion containing the integral lens. Molded within the column are ribs or vanes which strengthen the column. The tips of the ribs or vanes extend beyond the lens to act as stops which abut against the base plate housing. The portions of the ribs or vanes which extend beyond the lens also help ensure that the lens is an appropriate distance from the surface being read by the optical sensor.
In a pointing device assembly there are no special configurations of the PCB necessary to use the integrated aperture plate and lens. The optical sensor IC outfitted with the integrated aperture plate and lens is simply mounted to the PCB in the usual manner. By physically integrating the IC sensor and lens in this manner, several registration and alignment issues during the assembly process are nullified, and precision and repeatability are enhanced.